Controlled Growth of Quantum Dots and Nanopillars on Patterned GaAs Substrate by MOCVD

論文發表人：翁秉秀（新墨西哥大學光電所博士班）

 

http://www.tms.org/Meetings/Specialty/EMC07/home.html

 

本篇論文中，我們報告了以區域選擇性之奈米磊晶生長定址量子點及奈米柱。我們首先探討砷化銦量子點在砷化鎵金字塔結構奈米晶面上之選擇性結晶成核。此方式成長之量子點，其形狀和大小均較Stranski-Krastanow成長模式易於控制。砷化鎵金字塔結構是以金屬有機化學氣相沉積術在由二氧化矽定址之(001)砷化鎵基板上生長。圓形的定址區域是由干涉式微影術形成。砷化鎵金字塔結構由包含了{11n}、{10n}及(001)等三個晶面族的平衡晶體形狀組成。接下來的定址量子點結晶成核高度偏好(11n)平面，這是由於該平面提供較佳之能量最小化。在(11n)平面上形成之量子點的形狀十分容易預測，也十分均勻。這些砷化鎵平衡晶體形狀及高度晶面化之量子點均由高解析度之掃描式電子顯微鏡來分析。我們並且展示了常溫下之熒光光譜及電激發光譜，範圍在1.2到1.6微米之間。低溫的熒光光譜也證實了三維量子限制的存在。

同樣的定址方法也用於在砷化鎵(111)B基板上生長砷化鎵奈米柱。此方式提供較佳之均勻度及奈米柱之分布，同時還有簡易之電極接觸模式，因此是製作奈米電子元件一個有吸引力的方式。在這個研究中，奈米柱的生長在不同的生長條件下進行。這些奈米柱形成了高度結晶化、由(001)及(011)側面所包圍的六角截面。微熒光光譜及電氣特性也同時被檢視。

 

We report selective area nano-epitaxy to form both patterned quantum dots (PQDs) and nanopillars.  The selective InAs quantum dot (QD) nucleation on nano-faceted GaAs pyramidal facets is explored. This technique of QD growth enables better control of QD shape and size, than is possible with the Stranski-Krastanow (SK) growth mode. The GaAs pyramids are formed by metal-organic chemical vapor deposition (MOCVD) in patterned SiO₂ mask on a (001) GaAs substrate. The patterning is done by interferometric lithography and the circular patterns in SiO₂ are 25 nm deep and 230 nm in diameter, with a pitch of 330 nm. The GaAs pyramids are characterized by well-defined equilibrium crystal shapes (ECS) defined by three crystal plane families including {11n}, {10n} and (001).  Subsequent patterned QD (PQD) nucleation on the GaAs pyramidal facets is highly preferential towards the (11n) planes due to superior energy minimization and the shape of the QDs on the (11n) planes is also highly predictable and uniform.  The GaAs ECS pyramid and highly faceted PQDs are examined using high-resolution scanning electron microscopy (HRSEM), and room temperature photoluminescence (PL) and electroluminescence from 1.2 to 1.6 µm has been demonstrated. Three dimensional quantum confinement is confirmed with low temperature (77K) PL. 

The same lithographically defined patterns are used in the development of GaAs and GaSb nanopillars on GaAs (111)B substrates. The superior uniformity and arbitrary placement of the nanopillars along with easy electrical contacting schemes make these ensembles extremely attractive for nanoscale electronic devices. In this study, the nanopillar growth is conducted under a variety of conditions including III/V rations, substrate temperatures and growth rates.  Nanopillars exhibit highly crystallographic hexagonal cross-section formed by (001) and (011) sidewalls. Pillar dimensions are ~200 nm in diameter and > 2 um in length. Micro-PL and electrical properties of these wires are also investigated.